Sleep loss can severely impact on the integrity of cognitive functions. This review highlights the recent functional neuroimaging studies on the brain's response while performing cognitive tasks when deprived of sleep. Among sleep-deprived healthy volunteer s, reduced attention, accompanied by lowered parieto-occipital activation, may underlie performance decrements seen in other "higher cognitive domains". Functional neuroimaging in this setting has increased our understanding of how the brain responds to, and compensates for, sleep loss. Functional neuroimaging may also provide a safe, reproducible and non-invasive means to evaluate the cognitive and neural impact of therapeutic interventions designed to treat sleep disorders and/or to reduce the negative cognitive impact of sleep loss.